Pakkaus

import java.util.Scanner;

public class Pakkaus
{
    public static void main(String[] args)
    {
        Scanner inputTaker = new Scanner(System.in);
        String input = inputTaker.nextLine();
        
        StringBuilder answer = new StringBuilder();
        
        StringBuilder amountOfIterations = new StringBuilder();
        StringBuilder stringToIterate = new StringBuilder();
        
        for(int i = 0; i < input.length(); i++)
        {
            char characterAtI = input.charAt(i);
            
            if(("" + characterAtI).matches("[0-9]{1}"))
            {
                if(stringToIterate.length() > 0)
                {
                    int amount = stringBuilderToInt(amountOfIterations);
                    for(int j = 0; j < amount; j++)
                    {
                        answer.append(stringToIterate);
                    }
                    stringToIterate = new StringBuilder();
                    amountOfIterations = new StringBuilder();
                }
                amountOfIterations.append(characterAtI);
            }
            else
            {
                stringToIterate.append(characterAtI);
            }
            
            if(i == input.length() - 1)
            {
                int amount = stringBuilderToInt(amountOfIterations);
                for(int j = 0; j < amount; j++)
                {
                    answer.append(stringToIterate);
                }
            }
        }
        
        System.out.println(answer);
    }
    
    public static int stringBuilderToInt(StringBuilder stringBuilder)
    {
        int returnValue = 0;
        for(int i = 0; i < stringBuilder.length(); i++)
        {
            returnValue += Integer.parseInt("" + stringBuilder.charAt(i)) * Math.pow(10, stringBuilder.length() - 1 - i);
        }
        return returnValue;
    }
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: ACCEPTED

Test 12

Group: 3

Verdict: ACCEPTED

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED